Working on .Net with almost 5 years of exp now.
Speaking about .Net and Java , both are having excellent openings in industry. Market is full with Java as well as .Net developers. However , skilled developers are less in both.
So if you are really good at anyone of the programming languages, then you are good to go.
As i am on .Net track , will promote .Net

But choice is yours. Dont think too much about cross platform and as jobs are in ample amount for both, Make sure you sharpen your skills else you will be just another java or .net developer in market.
IMO, Java can give you more job opportunities as an enterprise software developer. But if you are planning to do freelancing, then .Net might be a better choice.
As Prime_Coder mentioned, being platform dependent is a BIG disadvantage of .Net.
It no way limits your earning or job opportunity.
@OP : Keep one thing in mind when asking such questions , everyone will promote their own field as they have experienced it.